The present invention relates to power transmission systems employing planetary speed reduction means, and more particularly to stepless speed change systems incorporating means operatively associated with the reduction means and adapted to transmit the torque of an input shaft to an output shaft with stepless speed change.
Stepless speed change systems are used as power transmission systems for agricultural, civil engineering and construction tractors, motor vehicles, tillers, combine harvesters and various other industrial machines.
Heretofore known as stepless speed change systems are hydraulic systems comprising a hydraulic pump and a hydraulic motor and mechanical gear systems. Hydraulic systems adapted for the transmission of great torque are expensive and inefficient, require special high-precision machining techniques and are prone to troubles due to the presence of extraneous solids in the oil.
On the other hand, conventional mechanical stepless speed change systems have a low torque transmitting capacity, involve noticeable slippage leading to inaccurate torque transmission and have structural limitations resulting in difficulties in making the overall system compact and inexpensive. Accordingly, it is difficult to install the mechanical system in tractors and like vehicles within the limited space of the housing.